What Does a JSON Validator Do?
A JSON validator checks your JSON text against the official JSON specification (RFC 8259) and tells you whether it is valid or not. If it finds a problem, it tells you exactly where the error is — which line and which column — so you can fix it without guessing.
JSONKit's validator at /json-validator checks your JSON as you type, with no button press needed. A green card means valid and shows the file size and line count. A red card means invalid, with the exact location of the problem.
The Most Common JSON Errors
Missing comma between properties — every property must be followed by a comma except the last one.
{
"name": "Ravi",
"age": 28
}Trailing comma after last item — JavaScript allows this, JSON does not. Remove the comma after the last property.
Single quotes instead of double quotes — JSON requires double quotes for both keys and string values.
Unquoted keys — in JavaScript objects you can write keys without quotes. In JSON every key must be a quoted string.
undefined, NaN and Infinity — these are valid JavaScript values but not valid JSON values. Use null instead.
Comments — JSON does not support // or block comments.
How to Read the Error Message
JSONKit shows a message like: Unexpected token at line 6, col 18. Line 6 is which line to look at. Col 18 is which character on that line, counting from 1 on the left. The error is usually at that character or just before it.
Validate JSON in Your Code
JavaScript:
try {
const data = JSON.parse(jsonString);
console.log("Valid:", data);
} catch (e) {
console.error("Invalid JSON:", e.message);
}Python:
import json
try:
data = json.loads(json_string)
print("Valid:", data)
except json.JSONDecodeError as e:
print(f"Invalid: {e.msg} at line {e.lineno}, col {e.colno}")Node.js (file):
const fs = require("fs");
try {
const data = JSON.parse(fs.readFileSync("data.json", "utf8"));
console.log("Valid");
} catch (e) {
console.error("Invalid:", e.message);
}JSON Schema Validation
Beyond syntax validation, you can validate the structure of your JSON using JSON Schema. This lets you specify which fields are required, what types they must be, and what values are allowed. JSONKit supports JSON Schema validation (draft-07 and 2020-12).